Definition

Periodic paralysis is a rare condition that is usually inherited. It causes occasional episodes of severe muscle weakness. The 2 most common types of periodic paralysis are
hypokalemic
and
hyperkalemic.

Causes

Periodic paralysis is a condition that is present from birth. Periodic paralysis is caused by abnormalities of the electrolyte channels on muscles.

Familial periodic paralysis is inherited, but may occur without a known family history. With the inherited form of the disorder, only 1 affected parent is needed to transmit the gene to the baby. Rarely, the condition occurs as a result of a noninherited genetic defect.

Risk Factors

Symptoms

Although muscle strength returns to normal between attacks, repeated episodes of weakness may lead to chronic muscle weakness later in life. The person remains alert and aware during attacks. There is no loss of sensation.

Episodes of severe weakness in the arms and legs are the major symptom. Typically, these episodes occur during sleep, early morning, or after strenuous activity. Cold, stress, and alcohol may also produce attacks. Other, less common, symptoms may include:

Weakness in the eyelids and face muscles

Muscle pain

Irregular heartbeats

Difficulty breathing or swallowing—This requires emergency care

Some features are specific to the type of periodic paralysis.

Hypokalemic:

Potassium levels
are low during attacks

Frequency of attacks varies from daily to yearly

Attacks usually last between 4-24 hours, but can last for several days

Attacks usually begin in adolescence, but they can occur before age 10

Hyperkalemic:

Potassium levels are high or normal during attacks

Attacks are usually shorter, more frequent , and less severe than the hypokalemic form; breathing and swallowing difficulties are extremely rare

Between attacks, patients often experience muscle spasms or difficulty relaxing their muscles, a condition is known as myotonia

Attacks usually begin in early childhood

Persons with some types of periodic paralysis are at risk for a condition known as malignant hyperthermia. This can occur during the use of
general anesthesia
. Anyone with a family history of periodic paralysis needs to notify the anesthesiologist of this history prior to any surgery.

Diagnosis

Because this primarily is an inherited condition, the most important part of diagnosis is obtaining a family history. You will be asked about your symptoms and your medical history. A physical exam will be done.

Your doctor may want to bring on an attack during an office visit. This should only be done under careful monitoring by an experienced neurologist. If an attack is triggered, several tests may be done, including:

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